The present invention relates to an electrical load controlling device, which is capable of detecting hunting and a short circuit. The present invention also relates to a hunting detecting method and a short circuit detecting method.
Typically, a driving force distributor of a four wheel drive vehicle directly transmits power from a transmission either to the front wheels or to the rear wheels, and distributes and transmits the power to the other ones of the front wheels and the rear wheels through a variable torque clutch mechanism. The transmitted torque is regulated for regulating the distribution of driving force to the front wheels and the rear wheels.
An electromagnetic type variable torque clutch mechanism is known in the art. An electromagnetic type variable torque clutch mechanism is controlled by a driving force distribution controlling device (ECU). By controlling a current value to an electromagnetic solenoid with the ECU, the frictional contact force between clutch plates is variably controlled. The engaging force of the clutch plates is controlled, accordingly. As a result, the transmitted torque is controlled.
Specifically, the ECU generates a current command value. To eliminate the deviation between the current command value and an actual current (detected current) supplied to the electromagnetic solenoid, the ECU computes the current command value and a duty ratio of the current command value through the PI control (proportional-plus-integral control) and the PWM control. The ECU then sends a control signal corresponding to the duty ratio to the drive circuit, thereby controlling the electromagnetic solenoid.
When there is malfunction of the electromagnetic solenoid due to a short circuit established between the terminals, and the ECU is sending out the control signal, an excessive current (actual current) flows if a field-effect transistor (FET) of the drive circuit is turned on. However, since the ECU is executing the PI control, the ECU lowers the duty ratio upon reception of an excessive actual current to control the electromagnetic solenoid such that the current is lowered to zero amperes 0A or a value close to zero amperes. When the current is lowered to zero amperes or the value close to zero amperes, the ECU executes a control for again flowing a current through the electromagnetic solenoid, which again causes an excessive current to flow. This dropping of the value of the current to zero amperes or to the value close to zero is called hunting.
Conventionally, a number of means for detecting current abnormalities such as an excessive current are known. However, these means operate on a logic designed for detecting a stationary abnormality, that is, a state in which a current is always more than a certain value. Therefore, these means cannot detect the above-noted hunting caused by a short circuit.